1. Field of the Invention
The present invention relates to a liquid property sensor.
2. Description of Related Art
Due to a soaring cost of fossil fuel, or for environmental protection, alcohol-blended fuel is getting to be widely used. The alcohol-blended fuel is produced by mixing alcohol into automotive fuel such as gasoline. When the alcohol-blended fuel is used, optimum combustion condition is varied in accordance with a mixture ratio between the alcohol and the gasoline. Therefore, in order to improve combustion efficiency, the mixture ratio between the alcohol and the gasoline needs to be detected in advance.
U.S. Pat. No. 5,367,264 (corresponding to JP-A-5-507561) discloses a detector for detecting alcohol content contained in air-fuel mixture by measuring a capacitance and a conductance of a capacitor. The detector includes a casing and a sensor element. The casing of the detector has a passage through which the air-fuel mixture passes, and the sensor element of the detector is exposed to the air-fuel mixture passing through the passage. The sensor element is arranged to be thermally and electrically insulated from the casing. The capacitor includes a first electrode made of a part of a wall of the casing, and a second electrode made of the sensor element exposed to flow of the air-fuel mixture.
A size of the above-described detector typically becomes large, so that an arrangement of the detector may become difficult. Further, the passage of the casing is complexly bending, and the sensor element is inserted into the passage with a predetermined clearance between an inner wall of the passage and the sensor element. Therefore, clogging of a foreign object may be easily generated.